Ever seen one of those thick, pea-soup nebulas in the Star Trek movies, Star Trek: The Next Generation or Star Trek: Voyager? That’s about the only place you’ll see them unless you are at ground-zero (space-zero?) of an exploding star. Nebulae are thin, wispy things that are best seen from a great distance with a powerful telescope and photographic film.
If you were inside a nebula, you could only tell because the brightness of the distant stars dim and your sensors would notice a higher density of particles and gas hitting your spacecraft’s hull. Maybe if you were floating outside your spacecraft in the shadow of your ship you would see a faint bluish or greenish mist at a great distance, but you’d have to stare at it for awhile. That’s because nebulas are gas and microscopic dust particles so thinly scattered you’d still call it a vacuum. They aren’t fog banks.
Now, if you were a handful of light-years away such that the nebula takes up your entire field of view, you’d see even less; especially if there are stars in the nebula. Your best view would be, again, in the shadow of your spacecraft looking towards the star at the center of the nebula. You’d see a faint blue-green mist, barely perceptible, extending around the star. If you took a camera and left the shutter open for a long exposure of the nebula, you’d get a nice photograph that looks like something you’d get from the Hubble.
OK, so if you’re even farther away, say the Earth, you still wouldn’t see anything spectacular. Here’s an experiment you can do at home. On a cold, clear night (like you get in January in North America) far away from city lights, look for the Orion Constellation. Just below Orion’s Belt (the three bright stars in a row in the middle of the constellation), there is a trio of objects in almost a straight line dangling from the Belt: this is the Sword of Orion. The middle object should look a little fuzzy, almost like a tiny fragment of cotton ball. That’s the Orion Nebula. Take a pair of binoculars or a telescope and look at it. You will see a bluish-white mist with several bright stars inside it. That’s what a nebula looks like to the naked eye. This is what the Orion nebula looks like to a telescope with a camera attached.
The reason you get the reds, oranges and yellow in pictures is because the human eye is sensitive to the blue-green part of the spectrum. Film stock and CCD have a better, more uniform range, of color sensitivity and can “see” the red and oranges and yellows. Also, for color-CCD observations, astronomers have been known to use image manipulation to crank up the red-yellow for aesthetic effect. Anything you see released from the Hubble Heritage group was made this way.